Technical Field of the Invention
The present invention is directed to methods and systems for evaluating the facial and dental features of a patient for orthodontic diagnosis and treatment. The present invention is directed to methods and systems for establishing a standard for alignment of dental features of a patient and to methods and systems for comparing the facial and dental features of a patient to the standard to assist in developing a treatment plan and evaluating progress during treatment.
Description of the Prior Art
Before Broadbent [1] Introduced cephalometric radiography in 1931, Orthodontic diagnosis depended on the orthodontist's clinical judgment of the patient's face and the malocclusion of the teeth. Milo Helman [2] did extensive work on photographic norms and advocated systematically measuring and analyzing the face. However, the introduction of radiographic cephalometrics overwhelmed those efforts.
Broadbent concluded that the Sella and Nasion (cephalometric landmarks) were the most stable parts of the area he exposed and suggested their use as stable reference points for diagnosing discrepancies and monitoring growth and treatment changes.
In 1953 Steiner [3] wrote, “It has been claimed by many that it is a tool of the research laboratory and that the difficulties and expense of its use in clinical practice are not justified. Many have argued that the information gained from cephalometric films, when used with present methods of assessment, do not contribute sufficient information to change, or influence, their plans of treatment.”
Since then, the cephalometric radiograph has been the subject of most of our diagnostic attention with analysis after analysis focusing on the cranial base as the reference for measuring deviations from what is referred to as the “Norm.”
Studies [4][5[6] have demonstrated individual variations in the orientation of the jaws and/or cranial base that make many of the classical measurements irrelevant. Sella and Nasion both show great individual variation in their position and Nasion continues to grow into a patient's teens. A low sella can result in a normally positioned maxilla having hypoplastic readings and a short cranial base can result in a class I skeletal relationship having class II measurements.
Others have suggested going back to traditional anthropological reference planes like Frankfort's Horizontal which was considered to best compromise for the orientation of crania of nonliving subjects. Moorrees [5] demonstrated that although Frankfort was relatively reproducible, it could vary up to 10 degrees from a living persons natural Orientation. Since we work with living individuals, he introduced orthodontists to the concept of Natural Head Position, which is determined by having a subject look at a distant object (e.g., the horizon) or his or her own eyes in a mirror. [6] This was shown to be reproducible to within 1-2 degrees and is considered the most accurate physiological reference line. True Horizontal as determined by Natural head positions was the bases for Moorrees's Mesh analyses which involved a scaled template of an ideal face that would be overlaid on the patient's face superimposing on Nasion and oriented according to Natural head position to visually determine the amount and location of dental and skeletal discrepancies. The distance between Sell and Nasion was used for scaling but the analysis did not really measure discrepancies relative to the position of landmarks inside the cranial base. The Concepts and ideas involved in this method provided orthodontists the tools to reduce their dependence on cephalometric radiography but still involved scaling to cranial base measurements and superimposing on Nasion which require radiographic exposure of the upper third of the face. Implant studies have also shown that Nasion experiences significant sutural growth in teenagers rendering the measurement of growth or treatment relative to it inaccurate.
Despite the progress Moorrees made in changing the paradigm, the profession reverted to its plaster models, its 2d photos and comparing radiographic measurements to reference values that do not necessarily represent what our patient populations seeks.
These so called “Norms” did not actually represent the average of the population and were almost all selected based on the author of a particular analysis's judgment of the occlusion and/or the face. Orthodontists may be the best candidates for judging the occlusion but their perception of facial esthetics can be influenced by their training and may not represent what the public finds attractive. This was demonstrated by Peck and Peck [7] in 1970 when they demonstrated that cephalometric measurements of people the public considered attractive at that time were generally “fuller and more protrusive” than the reference values of the commonly used cephalometric analyses.
Neotenized (childish) faces were found to be consistently more attractive regardless of the subject's actual age [8][9][10][11], and research has showed large agreement on characteristics of attractive faces across different racial and ethnic backgrounds. [12] Computer generated images with more average features were considered more attractive. [13] A composite formed by blending faces and averaging the features produced a face that was considered more attractive than most of the faces used to create it. However, in females enhancing certain female specific and species specific traits (e.g., smaller than average noses and chins, and higher than average foreheads) made the resulting face more attractive to males than the composite. Female preference for male faces was more variable and even varied with hormonal status, changes in the menstrual cycle, and contraceptive hormonal treatment. [14] Facial averageness and Symmetry were found to be attractive in Western and non-western cultures. Faces that were made more symmetric and closer to an average composite were considered more attractive and vise a versa. There was also no preference for own race composites over other races or mixed race composites. [15]
Several studies [7][6][17] have described soft tissue analyses. Most used two-dimensional images and several recent articles have used 3-dimensional images. The measurements performed generally resembled cephalometric measurements, and consistent statistically significant correlations were found between the cephalometric and soft tissue measurement. [18][19] Plooij [20] studied the reproducibility of 49 landmarks on 3D facial images and found that the intraobserver differences of 45 landmarks were less than 0.5 mm. The interobserver differences for 39 landmarks were less than 0.5 mm
In 2010, Bo{hacek over (z)}i{hacek over (c)} [21] presented a method of 3D soft tissue analysis that involved comparing patients to a 3D soft tissue template that was developed by averaging faces with class I occlusal relationships. Color-coding was used to mark parts of the face that deviated from the template used as the standard. The method described was a significant departure from the traditional diagnostic methods. However, like previous soft tissue analyses, the dentition was not evaluated within the context of the soft tissue making these methods adjuncts to cephalometrics and not potential replacements.
3D dental imaging has been available for over a decade and has been validated and widely accepted as an alternative to traditional casts for orthodontic diagnosis. [22][23]
Technology has evolved but orthodontists are essentially doing exactly what they did 80 years ago using computers to measure what they used to measure manually. Cephalometric radiographs continue to be the cornerstone of orthodontic diagnosis despite the fact that research has shown that cephalometric radiographs have no impact on treatment planning decisions regardless of the orthodontist's experience. [24]. An AJODO editorial reviewing recent radiation exposure guidelines for orthodontists mentions that there is no safe level of radiation exposure and that the benefits of diagnostic radiology usually outweigh the risks involved. [25] It concludes that there should not be a set of routine radiographs for all orthodontic patients, and that the risk involved is only justified when there is a health benefit to the patient from a minimum dose. It is unnecessary to take radiographs for routine investigation of TMD, for post treatment or prospective radiographs for medico-legal reasons, or for professional examinations. [25][26][27[ ]28][29]
Despite these guidelines some orthodontists [30][31][32] are advocating routinely exposing patients to many times the radiographic exposure of a cephalometric radiograph through cone beam imaging (68-368 μSv vs 30 μSv for a panoramic and cephalometric radiograph together). If every patient starting orthodontic treatment in the United States each year had one cone beam image instead of a cephalometric and panoramic radiograph, there would statistically be 10-80 additional cancer patients per year. [33][34][35] Most people advocating the use of cone beam radiographs end up converting them into 2-dimensional images and perform traditional cephalometric measurements so it is unclear why that would be expected to provide any more information than traditional cephalometric radiograph? Typical resolution is 0.3 to 0.4 voxels which results in lower resolution than traditional radiographs, greater error in identifying landmarks, underestimation of alveolar bone height, and overestimation fenestration and dehiscence. [36][37] They have limited usefulness even in patients with tempormandibular joint disorders since most of these are soft tissue in origin with radiographic changes usually appearing after the acute phase has passed. There is also no evidence to support that they aid in providing better treatment of these conditions. [38][39]
Two independent systematic reviews conducted in 2012 and 2013 [40][41] concluded that there is no high quality evidence to support the usefulness of cone beam imaging in orthodontics. In certain situation they can aid in the diagnosis and treatment of impacted teeth but even that could be done by only exposing the area of interest. [42]
Orthodontists are facing the same questions Cecile Steiner had to answer over 50 years ago. In a paper [43] that studied Head and neck organ radiographic doses, Hujoel et al. wrote: “Today, just like orthodontic radiography in the early 1900s, CBCT for orthodontic therapy is advocated by experts, without reliable evidence that the diagnostic technology is associated with improved patient outcomes.”
The area orthodontic treatment can influence is generally limited to the lower third of the face and if orthodontists are radiographically exposing the rest of the cranium to simply use it as a reference they need to stop and ask themselves if there is a deferent part of the face that can serve that purpose without the radiation involved in viewing the cranial base.
In late 2013 a systematic review44 evaluating orthodontic records concluded: “Cephalograms are not routinely needed for orthodontic treatment planning in Class II malocclusions, digital models can be used to replace plaster casts, and cone-beam computed tomography radiographs can be indicated for impacted canines. Based on the findings of this review, the minimum record set required for orthodontic diagnosis and treatment planning could not be defined.” They also mentioned that the influence of 3D facial imaging on diagnosis, treatment planning, and outcome assessment has not yet been evaluated. [44]